This scientist is racing to discover how gender transitions alter athletic performance—including her own

PORTLAND, OREGON, AND PHOENIX—Joanna Harper swallowed a few pills in late August 2004, a day after running in the Hood to Coast relay race between Oregon's highest mountain and the Pacific Ocean. They delivered a small dose of estrogen and a testosterone blocker and set in motion changes that Harper, who was designated male at birth and raised as a boy, had imagined since childhood. Harper's timing was deliberate—the 47-year-old nationally ranked runner wanted one more race before disrupting her hormones because she knew she'd never run as fast again.

The testosterone that courses through a man's body after puberty triggers and maintains a slew of physical changes: Men, whose levels of the hormone are usually some 10 to 15 times those of women, typically have larger muscles, denser bones, and higher fractions of lean body mass than women. That hormone-fueled transformation confers certain athletic advantages, and men on average run faster, lift more weight, and throw harder and farther than women. Sporting events are therefore usually split into male and female categories to ensure fair competition. But this division of the sexes, which has existed for as long as women have competed as athletes, forces an important question: Who, at least from an athletic standpoint, is female?

Many people believe transgender women such as Harper have athletic advantages over non-transgender women—sometimes called cisgender women—because of their previous exposure to male levels of testosterone. But Harper, a medical physicist at a large medical center in Portland, Oregon, has been challenging that assumption with data. In 2015, she published the first study of transgender athletes' performances, finding that transgender women who received treatment to lower their testosterone levels did no better in a variety of races against female peers than they had previously done against male runners. Although Harper's study included only a few transgender women, Eric Vilain of The George Washington University in Washington, D.C., a geneticist who specializes in gender-based biology, calls it "groundbreaking."

That work helped make Harper an unpaid adviser for sporting bodies, such as the International Olympic Committee (IOC), that are wrestling with transgender issues and other matters of gender. Although Harper has just a master's degree, she is helping spearhead several studies documenting how the physiology and performance of transgender athletes change as they make their transition.

Harper may not have the traditional pedigree of a scientist, Vilain says, but "her approach is highly respected." Harper has made "very important" contributions to understanding gender and sports performance, anticipating the debate that now swirls around transgender and "intersex" athletes, adds Stéphane Bermon, a sports physician and exercise physiologist at the Monaco Institute of Sports Medicine and Surgery.

A light at the end of the tunnel

In the 1960s, elite female athletes had to prove their sex by showing sporting officials their genitalia. Those unpopular "nude parades" were soon replaced by chromosomal tests, which had their own problems. Biology does not always cleanly divide human beings into two sexes. Some people, often described as intersex, have unusual sex chromosome arrangements or physical attributes such as ambiguous genitalia. Others have an innate sense of gender differing from the sex they were assigned at birth; they often choose to hormonally and/or surgically transition to the gender they identify as.

Harper, who grew up in Parry Sound, a small town about 250 kilometers north of Toronto, Canada, is among the latter. The oldest child of a high school teacher and a nurse, Harper wore her mother's and sister's clothing in private from a young age. Leaving elementary school one day, Harper asked a male friend an earnest question—had he ever thought, as Harper had, about being a girl? The boy recoiled. "It was clear from the way that my friend looked at me that I was never going to ask anybody that again," Harper says.

In high school, Harper threw herself into sports. She was best known as a star basketball player, averaging 18 points per game as a guard on the boys' team her senior year. But Harper was short for the men's college game. Instead, she ran track and cross-country as an undergraduate at what was then the University of Western Ontario in London, Canada, where she majored in physics. In 1982, Harper earned a master's degree in medical physics, training that prepared her to determine radiation treatment dosages for cancer patients. The career choice was, in part, lifestyle-oriented. "It was clear medical physicists were not putting in huge hours, and it would allow me time to run," she says.

It just blew me away, and it very much piqued my interest as a scientist.

Joanna Harper

Harper moved to Oregon a few years later to be closer to family in the Canadian province of British Columbia and to take a job in Portland. But her gender dysphoria always lurked. By 2004, "I was very close to a mental breakdown," she says. She started to see a therapist, who asked her to list what she'd lose if she transitioned genders. Near the top of that list was competitive sports—transgender athletes had no official opportunities to compete at the time.

Barely 3 months later, in May 2004, IOC announced a landmark ruling: Transgender athletes could participate in the Olympics. Strict stipulations were in effect for transgender women competing in women's events—they needed sex reassignment surgery, legal recognition of their gender by "the appropriate official authorities," and at least 2 years of verifiable hormone replacement therapy—but it was "a light at the end of the tunnel" for Harper. She wasn't an Olympic-level athlete, but she believed that change would trickle down to other sports organizations and she would be able to compete again.

Harper started hormone replacement therapy in August 2004. Spironolactone, a testosterone blocker and diuretic, flushed the testosterone her body was producing, and estradiol, a form of estrogen, began to make her form more typically feminine. In just a few weeks, Harper noticed changes such as breast tenderness and a decrease in body hair. The transition was a "very, very, very difficult time," Harper says. She lost most of her male friends, and her mother—her only living immediate family member—was not supportive. "When it became clear that I was going to go through with my transition, my mother said she never wanted to see me again," Harper recalls. Barbara Harper, who died in 2013, eventually relented, in a way. "When I visited, she didn't tell anyone who I was." "This is Joanna," was all her mother would say.

Today, the 61-year-old with collarbone-length red hair describes herself as a scientist, an athlete, and a transgender person—in that order. But being transgender can sometimes overshadow everything else. "We joke in the transgender world that if Hitler had been transgender, he would be described as ‘that transgender dictator.' That's the category that everybody wants to put you in."

Going to the science

In 1976, Renée Richards entered a New Jersey professional tennis tournament. Richards, who had enrolled at Yale University as Richard Raskind and captained its men's tennis team before undergoing sex reassignment surgery, was met with open hostility—more than 20 female players boycotted the competition in protest of her perceived advantages. Indeed, some physical attributes such as hand size and height—like Richards's tall frame—remain largely unchanged after hormone therapy, Harper says.

Many people expect other physical advantages to linger, too. Men generally have blood with higher oxygen-carrying capacity because testosterone stimulates bone marrow to produce more red blood cells, says Siddhartha Angadi, a cardiovascular physiologist at Arizona State University in Phoenix. Male bodies are also generally leaner, and carry less body fat—"an obvious benefit when it comes to athletic performance," Angadi says.

Some people therefore insist that transgender women and many intersex athletes competing in women's events will always have an unfair edge. (Little controversy exists over transgender men in sports, as many expect them to be at a disadvantage.) Others believe athletes should be able to compete in their self-identified gender without regulations. Harper wants to address the question with data. "You have to go to science."

Before her own transition in 2004, Harper expected that her 10,000-meter race time might increase by "a minute or two" as her testosterone level dropped and she slowed. But in less than a year, Harper was running a full 5 minutes slower than her personal best. "It just blew me away, and it very much piqued my interest as a scientist."

In 2005, Harper realized her experience wasn't unique after reading an article in Runner's World about another transgender female runner who had also become significantly slower. But when Harper searched for studies about the physiology of transitioning, she found none. So on nights and weekends, she began to moonlight on a research project.

Different, but same

A study of transgender women found their race times slowed after transitioning, but their age grades, which compare people to the best runners of the same sex and age, hardly changed, suggesting they have no advantage over non-transgender women.

Harper searched for transgender female distance runners willing to share race times from before and after their transitions. The transgender population, even now, tends to be "small and secretive," Harper says, and it took 7 years of contacting athletes through Yahoo and Facebook groups to collect data from eight runners. All the women had undergone hormone therapy to bring their testosterone levels in line with typical female levels. In Harper's study, titled simply "Race Times for Transgender Athletes" and published in 2015 in the little-known Journal of Sporting Cultures and Identities, she showed that all but one person ran substantially slower after transitioning.

Harper also calculated each subject's age grade, a common metric in track and field and distance running that reflects an athlete's performance compared with the fastest known time by someone of the same age and sex. Harper showed that the athletes' age grades before and after hormone therapy remained nearly the same. That is, the women were as competitive with their age- and sex-matched peers as they had been when competing against men. They weren't, in other words, likely to dominate women's races. "No one had previously looked at actual performance of transgender athletes pre- and posttransition," Vilain says.

Harper has since shown similar results for a transgender rower, a cyclist, and a sprinter. Together, the findings make a case that previous exposure to male levels of testosterone does not confer an enduring athletic advantage.

In 2015, IOC invited Harper to attend its Consensus Meeting on Sex Reassignment and Hyperandrogenism held in Lausanne, Switzerland. After 3 days, the panel of scientists and physicians converged on revised rules for transgender competitors, including at least 1 year of hormone replacement therapy for female competitors, rather than the 2 years previously required. That change was a nod to Harper's personal transition experience and to research published in 2004 in the European Journal of Endocrinology showing that the testosterone levels—and therefore performance—of 19 transgender women stabilized after 12 months of hormone therapy. The revised IOC policy also lifted the requirement for sex reassignment surgery. That decision was a long time coming, Harper says. "What your genitals are doesn't make a difference."

Less settled, however, is the debate about the appropriate upper limit of women's testosterone levels in elite athletic competition. The current IOC policy dictates that transgender women must have a testosterone level less than 10 nanomoles per liter, roughly the low end of typical male values. But because more than 99% of women have testosterone levels less than 3 nanomoles per liter, some researchers have suggested that limit is too high. Harper is among them. "If you're competing in the women's division, you should do so with women's hormone levels," she says. "I understand just how much difference they make."

South African runner Caster Semenya, who has always competed in women's races and won Olympic gold in Rio de Janeiro, Brazil, in 2016, recently refocused attention on the testosterone issue. In 2009, the International Association of Athletics Federations (IAAF)—the Monaco-based, world-governing body for track and field—controversially required her to take a sex-verification test after she breezed past competitors in the 800-meter race at the IAAF World Championships. The results, leaked during the competition, allegedly revealed that Semenya was intersex and had three times the testosterone of a typical woman. Neither she nor IAAF has ever confirmed that publicly, however.

In April, IAAF issued a policy that many groups—including Athletics South Africa, the country's athletics federation—view as targeting Semenya. It applies to women competing in certain track and field events, including those that Semenya excels at, who have specific intersex conditions in which their bodies produce and are sensitive to higher levels of testosterone. Drawing on performance and hormone data from an IAAF-sponsored study of athletes competing at its recent World Championships, which was published last year in the British Journal of Sports Medicine, the policy requires testosterone levels below 5 nanomoles per liter, half the previous IAAF threshold. The goal is "leveling the playing field to ensure fair and meaningful competition," IAAF President Sebastian Coe said in a statement.

In June, Semenya called that policy discriminatory and said she would challenge it at the Court of Arbitration for Sport. "I just want to run naturally, the way I was born," the 27-year-old told media. "I am a woman and I am fast." And earlier this month, three researchers who analyzed a subset of data from the 2017 study claimed to have found "significant problems and anomalies" and called for its retraction. IAAF updated the paper, but told The New York Times, which first reported the flap, that "the conclusions remain the same."

More controversy may be on the way: Within the next few months, IAAF is expected to issue updated testosterone-based regulations for transgender women as well. IOC also plans to announce new testosterone limits for athletes in women's events, which will be in effect for the 2020 Summer Olympics in Tokyo.

Research in transition

To get a clearer picture of how changing hormone levels affect an athlete's body, Harper and others want to collect data from people during their transitions. "It's important to know more about lean body mass; hemoglobin concentration; and psychological, endocrine, and metabolic changes during transition," says Bermon, who is also a scientific consultant for IAAF.

Harper recruited the athletes for the first such studies. One focuses on a 28-year-old distance runner named Lauren. (The athletes undergoing testing requested that only their first names be used in this story.) Roughly once a month, Lauren makes the 45-minute drive from her home in Queen Creek, Arizona, to downtown Phoenix to undergo a battery of tests in Angadi's lab.

He and his team have been measuring, among other things, the elasticity of Lauren's arteries, her bone density and distribution of fat, and how the myocardial fibers of her heart twist and untwist with each beat. After she started estrogen injections last fall, Lauren's blood pressure dropped by about 10 points and her body fat increased, Angadi says. Those changes are small, he cautions, and more measurements are needed. Another year of data may reveal a decline in bone density. "Bone is a really slow-turnover organ," he says.

During her visit in April, Lauren pulled on a bright blue mask that covered her nose and mouth, and Andrew D'Lugos, an exercise physiologist, had her start to run on a treadmill. "Way to go, Lauren!" "Enjoy the flat!" and "Looking good!" he and other scientists called out. D'Lugos cranked the treadmill up to 13, then 14 kilometers per hour. A large screen displayed Lauren's heart rate and oxygen consumption, new points popping up every 15 seconds. D'Lugos gradually increased the treadmill's incline, effectively forcing Lauren to run up an ever-steeper hill at her marathon pace. When at last she could go no farther, she pushed down on the treadmill's side railings, lifting her thin frame above the spinning black belt, her head bent in exhaustion.

No one had previously looked at actual performance of transgender athletes pre- and posttransition.

Eric Vilain, The George Washington University

Within 6 weeks after she started estrogen injections, Lauren's peak oxygen consumption rate—a measure of fitness—fell by 17%, the researchers reported at the American College of Sports Medicine's meeting in Minneapolis, Minnesota, in June. "She lost a fair bit of performance really quickly," Angadi says. But Lauren's fitness probably hasn't stabilized yet, he notes, because she only recently started to take a testosterone blocker. Angadi's team will test Lauren into 2019, when she runs the Boston Marathon. Charissa, a triathlete living in Colorado who is taking part in a similar study, lost roughly 15% of her aerobic capacity in 9 months since beginning hormone therapy, Harper reported in March at a British Association of Sport and Exercise Medicine conference held in Doncaster, U.K.

There, Harper announced that she and Yannis Pitsiladis—an exercise physiologist at the University of Brighton in the United Kingdom best known for his so-far futile efforts to train a man to run a marathon in less than 2 hours—plan to monitor roughly 20 men and 20 women as they transition. The largest study of its kind, it will recruit subjects from a London-based gender clinic and enlist the expertise of endocrinologists, muscle physiologists, and mental health professionals, among others. The undertaking will be enormous, Harper admits. "We're going to need help," she told the Doncaster audience. Pending research funding from the U.K. government, the study will begin in 2019.

Harper still has her day job, and she's writing a book about gender variance in sports. Fortunately, a refuge from all the demands on her time—and the controversies that come with her research—is just a block and a half from her front door. Several times a week, Harper turns left from her house toward Mount Tabor Park, one of Portland's largest. There, she runs 95 kilometers a week, often with friends, on trails that weave among 100-year-old cedar, spruce, and redwood trees. Just like the paths that sometimes open up to reveal fleeting views of Mount Hood in the distance, Harper's life has had its share of twists and turns. But she doesn't regret the decision she made 14 years ago. "I became a much happier person."